Mr Gore and Mr Bush reached this week's triumphs by different routes. Mr Gore began as an unimpressive and even vulnerable Democratic frontrunner but became stronger and infinitely more effective as the campaign moved towards his Super Tuesday obliteration of Bill Bradley.

Mr Bush, on the other hand, began as a seemingly irresistible Republican candidate with good positioning and stupendous resources, but reached this week's trouncing of John McCain only after big political and campaign costs. He is thought to have spent $60m (£36.5m), compared with Mr Gore's less than $40m.

The contrast between the winners' two campaigns is striking. Mr Bradley's threat peaked in late 1999, and although he and Mr Gore occasionally turned nasty in their televised debates earlier this year - and relations between the two men grew testy in private - their contest mostly remained within bounds.

Moreover, between New Hampshire and Super Tuesday, the Democratic rivals did not have to face a single primary contest. The Gore-Bradley contest was conducted at a distance, and with the polls showing the New Jersey senator slipping steadily out of contention. The final exchanges of the Democratic battle have been positively gentlemanly.

By contrast, Mr Bush and Mr McCain faced a succession of battles, which produced a vintage rollercoaster contest which was as closely fought as anything the Republican party has seen in a quarter of a century.

The Bush-McCain battle started out lighthearted but became increasingly intemperate in public and ruthlessly underhand in private. The threat to Mr Bush from the Arizona senator only became truly apparent with his win in New Hampshire - less than six weeks ago.

From then until now, both sides ploughed money into angry television ads and the Bush camp, in particular, seemed ready to enlist - or turn a blind eye to - any attack dog ready to take the field against Mr McCain.

Mr Bush has benefited from parallel efforts on his behalf by religious fundamentalists, anti-abortion lobbies, the tobacco industry and Texas financiers who underwrote last weekend's attack on Mr McCain's record on breast cancer and the environment.

Yet the reason why Mr Bush has won should not be mistaken. Though he certainly played dirty at times, he defeated Mr McCain because more Republicans in the overwhelming majority of the states believed he is their party's best chance of defeating Mr Gore in November. And, with his wins in big states like California, Ohio and New York, Mr Bush proved this week he has a claim which cannot be brushed aside.

Money remains the key to Mr Bush's campaign. By raising so much in the past, the Texas governor has been able to forgo the need to claim matching federal funding of his campaign - unlike Mr Gore or Mr McCain. This gives Mr Bush an advantage in the next phase of the battle, since he will be allowed to raise as much money as he can to fight the Democrats. Mr Gore, by contrast, will have to watch his wallet more cautiously.

On the Democratic side, Mr Gore has emerged as a truly formidable campaigner. The vice-president stumbled and bumbled on the campaign trail last year but the threat from Mr Bradley compelled him, last autumn, to shift gear and move his campaign home to Nashville. Since then he has not looked back.

Nevertheless, his victory was the direct and explicitly intended beneficiary of a reconfigured Super Tuesday primary system.

For years, the great fear of the vice-president's advisers had been that his path to the nomination would be bloody and lengthy. Accordingly, Mr Gore set out to stack the process against any potential rivals and to intimidate other contenders from venturing into the contest.

With Mr Gore's active involvement and support, the Democratic National Committee agreed in 1998 that the primary in California, the largest state in the union and the biggest must-win state for any presidential hopeful, should be moved up from its traditional position in June to the new date in March.

The idea was to make California and New York a citadel for Mr Gore, the establishment candidate. On Tuesday, the system worked perfectly for Mr Gore, who had made more than 60 visits to California during his seven years as vice-president, and who had sewn up the local party establishment there and in New York months ago.

Mr Gore won all 11 primary races on Super Tuesday, most of them by enormous margins. His win was a triumph for party machine politics of the highest order.

In the end, however, the central reason for Mr Gore's success is that no one in the Democratic party - and certainly not Mr Bradley - has been able to put together a compelling argument for the Democratic party to abandon either the politics or the politicians of the Clinton-Gore years. Mr Gore may not be the most thrilling candidate in the world, but he bestrides middle America on the issues which voters care about.